"Preface The work presented here summarizes the results of a scientific study performed by Prof. Dr. H.P. Lenz and Dipl.-Ing. Christian Cozzarini from the Institut f??r Verbrennungskraftmaschinen und Kraftfahrzeugbau at the Technische Universit?t Wien. The comprehensive text of all relevant work is contained in the studies ""Zur Bedeutung der Stickoxide"" (""About the Importance of Nitrogen Oxides"") and ""Emission@ Immission@ und Wirkung von Abgasbestandteilen"" (""Emissions@ Air Quality@ and Effects of Exhaust Gas Constituents"") published in 1993@ 1994@ 1995@ 1996@ and 1997 [40@ 47@ 60@ 143?C145]@ which summarize the present state of scientific knowledge based on more than 1@500 literature sources."